The timing and significance of gully incision on the eastern flank of the Faroe-Shetland Channel and its impact on seafloor infrastructure

Stewart, H.A.; Long, D..
2012
The timing and significance of gully incision on the eastern flank of the Faroe-Shetland Channel and its impact on seafloor infrastructure.
Near Surface Geophysics, 10 (4).
317-331.
10.3997/1873-0604.2012014

Abstract/Summary

The Faroe–Shetland Channel is an area of active offshore development and the safety of the seafloor infrastructure is paramount. This study has concentrated on a system of down-slope linear gullies and associated debris fans located to the west of Shetland in water depths of between 465m and 995m. Three-dimensional seismic, two-dimensional seismic and multibeam echosounder data have been combined to map the sea-bed morphology and shallow sub-surface geology associated with these features. The localised debris fans and gullies are interpreted as the products of high energy mass-flow fed by an ancient ice-stream constrained to this part of the West Shetland Shelf. During decay of this ice-stream, melt-water plumes of sediment released from the retreating ice front have formed a thin (<5m) laminated sediment drape overlying the debris fans observed from seismic data. At present locally strong oceanic currents rework and redistribute sea-bed sediments into sediment drifts called contourites that cover much of the sea bed of the Faroe–Shetland Channel. These along-slope deposits have been shown to infill erosional features located further northeast along the continental slope, however, these deposits thin to the southwest reflecting the increasing strength of present day oceanic currents impeding deposition. This study shows that slope angles within the down-slope gullies exceed 20° and cut down into earlier contouritic sediments. The high slope angles recorded on the multibeam echosounder data combined with video data confirm the presence of near-vertical sediment cliffs within the gullies. This is of significance to industry as there are currently producing hydrocarbon fields and continued exploration in and around these sea-bed features.